Method of making a normally liquid fuel interchangeable with gas



ID FUEL Dec. 13, 1966 J. W. STOOPS OF MAKING A NORMAL-LY LIQU INTERGHANGEABLE WITH GAS Filed Jan 28, 1966 METHOD mo 6 W m V w m Q m o mo m m E V A cwaohzz m uwm M. 9. a Eawwmi mm 65am 555m new ld INVENTOR BY JAMES W. STOOPS A TTOR NEY United States Patent C) 3,291,191 METHOD OF MAKING A NQRMALLY LIQUID FUEL INTERCHANGEAELE WITH GAS James W. Stoops, Thornhury, Pa., assignor to Sun Gil Company, Philadelphia, Pa, a corporation of New .lersey Filed Jan. 28, 1966, Ser. No. 530,761 5 Claims. (Cl. 158-1175) This application is a continuation-impart of copending application Serial No. 230,204, filed October 12, 1962, now abandoned.

This invention relates to a method of making a normally liquid fuel interchangeable with gas.

The cost of guaranteed continuous gas service from a utility is much higher than the cost of interruptible gas service. When interruptible service is used it is necessary to shut down operations requiring gas heat or to change over to a standby fuel on short notice in order to keep operating.

Liquid petroleum gases such as propane and butane, fuel oils such as gasoline and gases made by cracking hydrocarbon oils, i.e. oil gas, have been used as alternative fuels. Liquidified petroleum gases are very satisfactory from the standpoint of performance in the gas burner itself since they provide a clean radiant flame like that of natural gas. However, propane vaporizes at about 40 F. and butane at about 32 F. When it is kept in mind that atmospheric temperatures can vary from 20120 F. at the same location, it can be seen that the storage and handling problems associated with liquified petroleum gases are acute. The usual recommendations are that butane be stored at a pressure of 2580 p.s.i.g. and propane at 25l80 p.s.i.g., and these pressures require expensive and complicated equipment for storage, transportation and meeting fire underwriter requirements. Fuel oils contain heavy ends which give a dirty flame and generate deposits of soot and coke. The heavier fuel oils cannot be used without special vaporizing, metering and burner elements. The manufacture of oil gas requires cracking facilities.

The object of this invention is to provide a method of operating a gas burner in interruptible service with a fuel which is interchangeable with natural gas. Another object of the invention is to provide a standby fuel which requires no special storage or transportation equipment, which is a liquid at ambient temperatures and pressures and which vaporizes essentially completely with or without the application of external heat. Still another object of the invention is to provide a hydrocarbon vapor which can be introduced into a gas burner without changing or modifying the gas burner and which burns with a clean blue radiant flame of generally the same quality and characteristics as the game flame it replaces. This type of flame is required for bakery ovens, in glass polishing equipment, soldering equipment, and other units which require a clean flame which can be precisely adjusted.

The objects of our invention are accomplished by operating a gas burner with vapor prepared from a particular liquid paraffinic light petroleum hydrocarbon fraction. The fraction can be produced at relatively low cost. In one embodiment the base fraction is the raffinate from a solvent extraction process designed to extract aromatic hydrocarbons from a petroleum refinery stream. This base fraction is primed with propane, butane, pentane or a mixture of these so that the final fraction contains from 120 volume percent of these materials. It should be noted that when propane and butane are thoroughly mixed in the fraction they do not vaporize rapidly out of the mixture at low pressures, thus the fraction does not have the disadvantages inherent in propane, butane Patented Dec. 13, 1866 and mixtures thereof. The source of the components blended to prepare the liquid hydrocarbon fraction is not critical so long as the final fraction obtained meets the specifications set forth below. Selected fractions from distillation, solvent extraction, reforming and chemical treating are suitable. These fractions can be pretreated in any suitable conventional manner to remove organic and inorganic contaminants like aromatic hydrocarbons, olefins, polymers, gum, sulfur, organo metallic com pounds, etc.

The fraction is essentially paraffinic in that it is composed principally of saturated aliphatic and alicyclic hyrocarbons. These can be substituted with alkyl groups. The majority of the saturated hydrocarbons are aliphatic hydrocarbons i.e. paraffins and isoparaffins, having 5 or more carbon atoms. The fraction does not contain more than 25 volume percent of aromatic and olefinic hydrocarbons. That is, it contains at least volume percent saturated hydrocarbons i.e. 75 to 100 volume percent, preferably 90 to 100 volume percent saturated hydrocarbons. At least 50 volume percent of the fraction consists of aliphatic hydrocarbons having 5 or more carbon atoms. These are mostly paraffins and isoparaflins having 5 to 8 carbon atoms in the molecule. The fraction has an API gravity ranging from about 60 to about egrees, and an end boiling point of up to about 450 F. (preferably about 200450 F.). A particularly suitable fraction would be one having an initial boiling point ranging from about 150 F. and an end boiling point ranging from 200350 F. It is usually almost waterw-hite in color. The Reid vapor pressure at F. ranges from 3.0 to 16.0 psi. It is essentially sulfur-free and has a Conradson carbon value of 0.

The petroleum fraction can be transported and stored at pressures ranging from atmospheric to superatmospheric pressure as known in the prior art. Extremes of daily temperature variation and proximity to equipment evolving some heat do not affect the storage stability and safety features of the fuel to the extent that such conditions affect normally gaseous fuels.

A particular advantage of the fuel is the ease with which it is vaporized. Although the liquid has an end boiling point of up to about 450 F., it can be injected into a stream of carrier gas, preferably air at temperatures of 30-300 F. and fed to a gas burner without drop out of liquid. The fuel forms a homogenous true vapor which passes into the burner and burns with a precise steady flame.

In vaporizing the liquid fraction, temperatures as low as 30 F. can be used. At lower temperatures, by varying the quantity of air with respect to the quantity of fuel sprayed into the air stream, the partial pressure effect of the fuel in the resulting vapor contains the proper amount of vaporized liquid to provide a gas burner fuel. Therefore, vaporization temperatures of from about 30 F. to about 300 F. are suitable. The preferred range is 40-250 F. These temperatures are well below autoignition and cracking temperatures.

In the accompanying drawing:

FIG. 1 is a diagrammatic illustration of one form of apparatus for carrying out the method by using premix gas; and

FIG. 2 is a digrammatic illustration of another form of apparatus for carrying out the method without using premix gas.

The method of the invention can be applied to any gas apparatus capable of employing a vapor fuel. One form of apparatus is shown in FIGURE 1 of the accompanying drawing. Liquid fuel at ambient temperature (about 70 F.) is supplied to line 1 at atmospheric pressure from storage tank 2. The tank is also at atmospheric pressure.

A positive pressure (1-5 p.s.i.g.) can be applied to the tank if desired. The liquid fuel has the following properties:

Gravity API 70.0 Distillation values:

IBP F 100 50% F 200 90% F 230 HP F 300 Reid vapor pressure (100 F.) p.s.i.g-- 5.5-7.0 Sulfur wt. percent 0.005

Hydrocarbon composition Paraflins Vol. percent C 3.1

Total 78.7 Naphthenes 12.7

Total saturates 91.4

Total aromatics 5.6 Total olefins 3.0

Line 1 contains variable speed positive displacement pump 3, flow meter 4, relief valve 5, pressure gauge 6, globe valve 7 and terminates in spray nozzle 8. Compressed premix gas, preferably air is supplied by lines 9 and 10 to vaporizer tube 11. Line 9 contains globe valve 12. Nitrogen from line 13 containing globe valve 14, is used to sweep the system. Line 10 contains pressure regulator 15, needle valve 16, flow meter 17 and check valve 18.

The fuel is sprayed countercurrently into the air stream. The nozzle is centrally located in the vaporizer tube. Liquid fuel is supplied at the rate of .1 to .7 gal/hr. and air is supplied at the rate of 4 to 40 ftfi/hr. Fuel concentration in the premix air can vary from 12% to 40 vol. percent based on total fuel mixture.

Vaporizer tube 11 is a 1%" x 4 copper pipe and it is wrapped with a 110 volt Nichrome resistance heater 19. The mixture of vaporized fuel and air is heated to a temperature of about 160-200 F. as measured by temperature gauge 20. The mixture was passed through two 90 degree bends 21 and 22 at the end of vaporizer tube which serve as a liquid drop to drop, out any liquid fuel could not be maintained in the vapor state. In a run of about 180 minutes duration, no liquid was obtained when drain 23 was opened. Gauge 24 records the pressure downstream of the trap and is a measure of orifice pressure. Pressures range from 0-7 p.s.i.g.

'The vaporized fuel-air mixture is passed through line 25 containing plug valve 26 and inspirator 27 consisting of adjustable primary air control 28 and nozzle 29 into a ribbon gas burner 30. Natural gas is supplied by line 31 containing valve 32 and the two fuels can be supplied to the burner interchangeably by opening and closing the proper valves in the system. In making the change it is not necessary to change primary air settings or to modify the burner orifice. If desired, the change-over can be accomplished by automatic devices known in the art.

FIGURE 2 discloses a method and apparatus for op erating a gas burner on a vaporized liquid fuel without employing premix gas to vaporize the liquid. The liquid fuel can be the same as the fuel described previously. The fuel is passed from tank 101 by line 102 to the burner without vaporizing it. Line 102 contains pump 103, flow meter 104, bypass valve 105, pressure gauge 106 and globe valve 107. The line terminates in nozzle 110. The nozzle feeds a spray directly into the burner. The liquid fuel can be heated, but this is not necessary. Supplementary primary air from line 111 is mixed with the fuel spray issuing from the nozzle. The pressure at the nozzle can be 0-100 p.s.i.g. The primary air can be heated or not as desired, air temperatures of 50400 F. being satisfactory. The air pressure can range from 15-100 p.s.i.a. Suflicient air is added to provide a ratio of about 1200 cubic feet of air per gallon of oil. This ratio will provide a combustion mix containing 2 to 20 vol. percent vaporized oil based on the total mix. In the embodiment shown in FIGURE 2 nozzle and air line 111 replace the gas orifice and inspirator. Although this embodiment requires an equipment change, it eliminates a vaporizer and premixing with carrier gas.

The above description shows that a gas fuel can be burned interchangeably in a unit which normally burns gas without the use of large amounts of special equipment for operating on the liquid fuel. The method features quick change-over from gas to liquid and vice versa because a single common burner head and mixing chamber can be used. The orifice nozzle does not accumulate coke and clog up after many cycles of alternating gas and liquid feeds.

The flame quality is consistent under both types of operation usually without adjustment of primary air settings. The flame is clean and blue with little or no yellow tipping. No lift off or flashback problems are encountered, and it is believed that this is due to a faster flame speed. The B.t.u. release above the burner seems to be superior to that of gas.

A gas burner rated at 36,000 B.t.u./hr. (gas) can be operated at from 12,000 to 106,000 B.t.u./hr. on vaporized liquid fuel. When using gas the operator has only one degree of freedom in controlling combustion i.e. gas pressure. The liquid feed of the present invention provides two degrees of freedom in that both pressure and the proportion of liquid fuel in the fuel air mixture can be varied by the operator.

Obvious variations are intended to be included within the scope of the disclosure and claims. The method is applicable to conventional gas burners generally. When the liquid fuel is vaporized in contact with a gas, any suitable premix or carrier gas can be used including air, oxygen enriched air, nitrogen, helium, CO CO, steam flue gas and others as well as mixtures of these.

Heat may be applied to any fuel component or apparatus element by direct heating or by recycle.

Startup, change-over and shut-down can be controlled automatically by employing known electrical, mechanical, or combination devices.

The invention claimed is:

1. A method of operating a gas burner in interruptible service comprising the steps of a. terminating the flow of gas to the burner,

b. supplying a normally liquid paraffinic light petroleum hydrocarbon fraction from storage,

c. mixing the fraction at a temperature in the range of 30 to 300 F, with primary air,

(1. and burning the fraction in the burner to provide a clean blue radiant flame having characteristics and quality generally equivalent to the gas flame,

said petroleum hydrocarbon fraction having an end boiling point of up to about 450 F., and containing at least 75 volume percent saturated hydrocarbons containing 5 or more carbon atoms and less than 25 volume percent aromatics and olefins.

2. A method of operating a gas burner in interruptible service comprising the steps of a. terminating the flow of gas to the burner,

b. supplying a normally liquid paraffinic light petroleum hydrocarbon fraction from storage to a vaporizing zone,

c. spraying the liquid hydrocarbon fraction in said zone countercurrent to a stream of premix gas,

d. heating the atomized liquid-gas mixture at a temperature in the range of 30 to 300 F. to substantially completely vaporize said mixture,

e. mixing the vapor with primary air employing the same inspirator used for gas,

f. and burning the vapor in the burner to provide a clean blue radiant flame having characteristics and quality generally equivalent to the gas flame,

said petroleum hydrocarbon fraction having an end boiling point of up to about 450 F., and containing at least 75 volume percent saturated hydrocarbons containing 5 or more carbon atoms and less than volume percent aromatics and olefins.

3. A method of operating a gas burner in interruptible service comprising the steps of a. terminating the flow of gas to the burner,

b. removing the gas inspirator and substituting therefor an atomizing nozzle and supplementary primary air pp y,

0. supplying a normally liquid paraffinic light petroleum hydrocarbon fraction from storage,

d. spraying the hydrocarbon fraction at a temperature of to 300 F. through an atomizing nozzle directly into the burner at a nozzle pressure ranging from 0 to 100 p.s.i.g.,

e. mixing the vapor with primary air and supplementary primary air supplied at a temperature in the range of to 400 F. and a pressure in the range of 15 to 100 p.s.i.a.,

f. and burning the vapor-air mixture in the burner to provide a clean blue radiant flame having characteristics and quality generally equivalent to the gas flame,

said petroleum hydrocarbon fraction having an end boiling point of up to about 450 F., and containing at least volume percent saturated hydrocarbons containing 5 or more carbon atoms and less than 25 volume percent aromatics and olefins.

4. A method according to claim 2 wherein the petroleum hydrocarbon fraction has an initial boiling point ranging from about to F. and an end boiling point ranging from 200 to 350 F.

5. A method according to claim 3 wherein the petroleum hydrocarbon fraction has an initial boiling point ranging from about 90 to 150 F. and an end boiling point ranging from 200 to 350 F.

ReferencesCited by the Applicant UNITED STATES PATENTS 1,364,972 1/1921 Andersone et al. 1,903,583 4/1933 Watkins. 2,163,871 6/ 1939 Diescher. 2,607,671 8/ 1952 Van Heeckeren et a1. 2,734,809 2/ 1956 Pettyjohn et al. 2,772,952 12/1956 Jacobs. 2,871,254 1/1959 Hoo-g et al. 3,060,116 10/1962 Hardin et a1.

JAMES W. WESTHAVER, Primary Examiner, 

1. A METHOD OF OPERATING A GAS BURNER IN INTERRUPTIBLE SERVICE COMPRISING THE STEPS OF A. TERMINATING THE FLOW OF GAS TO THE BURNER, B. SUPPLYING A NORMALLY LIQUID PARAFFINIC LIGHT PETROLEUM HYDROCARBON FRACTION FROM STORAGE, C. MIXING THE FRACTION AT A TEMPERATURE IN THE RANGE OF 30* TO 300*F. WITH PRIMARY AIR, D. AND BURNING THE FRACTION IN THE BURNER TO PROVIDE A CLEAN BLUE RADIANT FLAME HAVING CHARACTERISTICS AND QUALITY GENERALL EQUIVALENT TO THE GAS FLAME, SAID PETROLEUM HYDROCARBON FRACTION HAVING AN END BIOLING POINT OF UP TO ABOUT 450*F., AND CONTAINING AT LEAST 75 VOLUME PERCENT SATURATED HYDROCARBONS CONTAINING 5 OR MORE CARBON ATOMS AND LESS THAN 25 VOLUME PERCENT AROMATICS AND OLEFINS. 